Patent application title: SYSTEM FOR DETERMINING THE POSITION OF A MOVABLE MEMBER

Abstract:

A first magnet is secured to the movable member at a first axial position
and is associated with a first magnetic field. A secondary magnet is
secured to the movable member at a secondary axial position and is
associated with a secondary magnetic field. A sensor assembly comprises
magnetic sensors arranged in an array (e.g., on a fixed member). A first
magnetic sensor is spaced apart from the sensor assembly such that the
first magnetic sensor detects the first magnetic field of the first
magnet in a first state and an absence of or change in the first magnetic
field in a second state. A data processor is arranged for determining an
axial position of the moveable member based on at least one of the
magnetic fields sensed by the sensor assembly.

Claims:

1. A system for determining the position of a movable member with respect
to a fixed member, the system comprising:a movable member capable of
axial movement within a range of axial positions;a first magnet secured
to the movable member at a first axial position and associated with a
first magnetic field;a secondary magnet secured to the movable member at
a secondary axial position and associated with a secondary magnetic
field;a sensor assembly comprising magnetic sensors arranged in an array
on a fixed member;a first magnetic sensor spaced apart from the sensor
assembly on the fixed member such that the first magnetic sensor detects
the first magnetic field of the first magnet in a first state and an
absence of the first magnetic field in a second state; anda data
processor for determining an axial position of the moveable member based
on at least one of the first magnetic field and a secondary magnetic
field sensed by the sensor assembly.

2. The system according to claim 1 wherein a shift between the first state
and the second state of the first magnetic sensor indicates at least one
of a direction or magnitude of displacement of the movable member with
respect to the fixed member.

3. The system according to claim 1 wherein the data processor uses at
least one of a magnitude and an orientation of the magnetic field
detected by each magnetic sensor in the sensor assembly to determine the
axial position of the movable member with respect to the fixed member.

4. The system according to claim 1 wherein the magnetic field sensors of
the sensor assembly comprise analog magnetic sensors.

5. The system according to claim 1 wherein the array is arranged in a
generally linear series with each magnetic field sensor interspaced
approximately a uniform amount from an adjacent magnetic field sensor in
the array.

6. The system according to claim 1 wherein the first magnetic sensor
comprises a digital magnetic field sensor.

7. The system according to claim 1 further comprising:a signal
conditioning circuit coupled to the sensor assembly, the signal
conditioning circuit amplifying the sensor signals to fall within a
certain amplitude range and filtering noise from the sensor signals.

8. The system according to claim 1 further comprising:a data storage
device for storing reference magnitude and angle data for the magnetic
fields associated with known axial positions of the movable member;a
position detection module for comparing the observed magnitude and angle
data for at least one of the magnetic fields to identify a match between
the observed magnitude and angle data and the reference magnitude and
angle data; the position detection module capable of identifying the
axial position of the movable member associated with the match.

9. A system for determining the position of a movable member, the system
comprising:a movable member capable of axial movement within a range of
axial positions;a first magnet secured to the movable member at a first
axial position and associated with a first magnetic field;a second magnet
secured to the movable member at a second axial position and associated
with a second magnetic field;a third magnet secured to the movable member
at an intermediate axial position between the first axial position and
the second axial position, the third magnet associated with a third
magnetic field;a sensor assembly comprising analog magnetic sensors
arranged in an array, the sensor assembly aligned with the intermediate
axial position of a movable member when the movable member is in an
intermediate position within the range of axial positions;a first
magnetic sensor spaced apart from the sensor assembly such that the first
magnetic sensor detects the first magnetic field when the movable member
is in the intermediate position, the first magnetic sensor having a first
state indicative of one direction of displacement of the movable member;a
second magnetic sensor spaced apart from the sensor assembly such that
the second magnetic sensor detects a second magnetic field when the
movable member is in the intermediate position, the second magnetic
sensor having a second state indicative of an opposite direction of
displacement of the movable member; anda data processor for determining
an axial position of the moveable member based on at least one of three
magnetic fields sensed by the sensor assembly and the states of the first
and second magnetic sensors.

10. The system according to claim 9 wherein the sensor assembly comprises
a plurality of analog sensors arranged in a generally linear array.

11. The system according to claim 9 wherein the first magnetic sensor
comprises a digital magnetic field sensor and wherein the second magnetic
sensor comprises a digital magnetic field sensor.

12. The system according to claim 9 wherein for a small displacement of
the movable member from the intermediate position, the first state and
the second state are active, indicating a detection of the first magnetic
field and the second magnetic field.

13. The system according to claim 9 wherein for a larger displacement of
the movable member from the intermediate position, one of the first state
and the second state are active and one of the first state and the second
state are inactive.

14. The system according to claim 9 wherein the sensor assembly is aligned
for detection of the first magnetic field when the movable member
approaches one end within the range of axial positions.

15. The system according to claim 9 wherein the sensor assembly is aligned
for detection of the second magnetic field when the movable member
approaches another end within the range of axial positions.

Description:

FIELD OF THE INVENTION

[0001]This invention relates to a system for determining the position of a
movable member.

BACKGROUND OF THE INVENTION

[0002]A position sensor may detect the position of a movable member. For
example, the position sensor may detect the position of a movable rod,
piston, or another movable member with respect to a cylinder (e.g.,
hydraulic cylinder). The detected position may provide feedback,
indirectly or directly, to an actuator associated with the movable member
to precisely control the position or movement of the movable member at a
corresponding time. The precision or accuracy of the position sensor may
be degraded by any of the following factors: environmental stress,
thermal stress, shock and vibration, and aging of components of the
position sensor. Therefore, there is a need for a position sensor that
determines the position of a movable member with enhanced precision or
accuracy that addresses one or more of the above factors.

SUMMARY OF THE INVENTION

[0003]A system for determining the position of a movable member with
respect to a fixed member comprises a movable member capable of axial
movement within a range of axial positions. A first magnet is secured to
the movable member at a first axial position and is associated with a
first magnetic field. A secondary magnet is secured to the movable member
at a secondary axial position and is associated with a secondary magnetic
field. A sensor assembly comprises magnetic sensors arranged in an array
(e.g., on a fixed member). A first magnetic sensor is spaced apart from
the sensor assembly such that the first magnetic sensor detects the first
magnetic field of the first magnet in a first state and an absence of or
change in the first magnetic field in a second state. A data processor is
arranged for determining an axial position of the moveable member based
on at least one of the first magnetic field and the secondary magnetic
field sensed by the sensor assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004]FIG. 1A is a block diagram of one embodiment of a system for
determining the position of a movable member.

[0005]FIG. 1B is an illustration of a side view of movable member and
various magnetic field sensors in accordance with the embodiment of FIG.
1A.

[0006]FIG. 2A is a block diagram of one embodiment of a system for
determining the position of a movable member.

[0007]FIG. 2B is an illustration of a side view of movable member and
various magnetic field sensors in accordance with the embodiment of FIG.
2A.

[0008]FIG. 3 is a block diagram of another embodiment of a system for
determining the position of a movable member.

[0009]FIG. 4 is a block diagram of another embodiment of a system for
determining the position of a movable member.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0010]In accordance with one embodiment of the invention, FIG. 1A and FIG.
1B show a system 11 for determining the position of a movable member 40
(in FIG. 1B) with respect to a stationary or fixed member 38. In FIG. 1B,
a first magnet 42 and a secondary magnet 146 are secured to the movable
member 40 and spaced apart from one another.

[0011]In FIG. 1A, the position detection system 11 comprises a group of
magnetic field sensors: a first magnetic sensor 32 and a sensor assembly
34. The first magnetic sensor 32 may be coupled to a data bus 16. The
sensor assembly 34 has one or more sensor outputs coupled to a signal
conditioner 28. The signal conditioner 28 is coupled to an
analog-to-digital converter 24. In turn, the analog-to-digital converter
24 is coupled to a data bus 16.

[0012]A data processor 20 can communicate with one or more of the
following components via the data bus 16: the first magnetic sensor 32,
the analog-to-digital converter 24, a data storage device 10 and a
communications interface 14. As illustrated in FIG. 1A, the data
processor 20, the data storage device 10, and the communications
interface 14 are coupled to the data bus 16. The data processor 20
comprises a position detection module 22. The data storage device 10 may
store position data 12 or calibration data 13, or both, determined by the
data processor 20 or position detection module 22.

[0013]The first magnetic sensor 32 may comprise one or more of the
following: a digital magnetic field sensor, an analog magnetic field
sensor with an integrated analog-to-digital converter 24, a
magneto-resistive sensor, Hall-effect sensor, a linear position magnetic
sensor, or an angular position magnetic sensor. In one embodiment, a
digital magnetic field sensor has one of two discrete states or output
levels. For example, the output levels (e.g., voltage levels or logic
levels) may represent a low logic level (e.g., 0) or a high logic level
(e.g., 1). In one configuration, the output level of the first magnetic
sensor 32 provides a signal or data output that indicates whether or not
a magnet (e.g., first magnet 42 or secondary magnet 146) of the movable
member 40 is in close proximity to the first magnetic sensor 32. The data
output of the first magnetic sensor 32 may be used to determine the
direction of displacement of the movable member 40 or whether the axial
position or positions detected by the sensor assembly 34 are within a
first range of axial positions or a second range of axial positions. The
first range of axial positions are generally distinct from the second
range of axial positions, although the two ranges may be contiguous or
overlapping, where overlapping provides additional redundancy and
potential increased accuracy.

[0014]In a first exemplary configuration, the first magnetic sensor 32 has
a digital output, where a first state indicates that a magnetic field
(e.g., first magnetic field 55 of a first magnet 42) meets or exceeds a
threshold magnetic field strength, and where a second state indicates
that the magnetic field (e.g., the first magnetic field 55) is less than
the threshold magnetic field strength or that no detectable magnetic
field is present.

[0015]In a second exemplary configuration, the first magnetic sensor 32
has a first state indicative of movement of the movable member 30 in one
direction (e.g., a known direction) of displacement of the movable member
40. The direction of displacement may be known based on the configuration
(e.g., separation and position) of the magnets on the movable member 40,
for example.

[0016]The sensor assembly 34 comprises an array of magnetic field sensors
secured to a fixed member 38. For example, the sensor assembly 34
comprises a generally linear array of magnetic field sensors, where each
sensor is separated from an adjacent sensor by a known or fixed interval.
Each magnetic field sensor within the sensor array or sensor assembly 34
may comprise an analog sensor, a magneto-resistive sensor, a Hall-effect
sensor, a linear position magnetic sensor, or an angular position
magnetic sensor. In one embodiment, the output of each analog sensor is
proportional to the magnetic field (e.g., from one or more magnets 42 or
146 on the rod) and can be used to determine a position of the movable
member 40 with a resolution that is much smaller than the distance
between two sensors (e.g., typically 50 micrometers for a 10 mm pitch)
within the sensor assembly 34 on the movable member.

[0017]In one embodiment, the signal conditioner 28 has conditioner inputs
for receiving sensor data from each magnetic sensor in the sensor
assembly 34. The signal conditioner 28 may provide one or more of the
following: (a) amplification (e.g., or attenuation) of the sensor signals
of the sensor assembly 34 by a target amplification level, to a target
signal level or to a target signal level range, (b) filtering noise from
the sensor signals of the sensor assembly 34, and (c) biasing the sensors
of the sensor assembly 34 in an appropriate mode (e.g., in a saturation
mode or with an appropriate level of direct current (DC) bias). The
signal conditioner output is coupled to the input of the
analog-to-digital converter 24.

[0018]The analog-to-digital converter 24 converts any analog signals
provided by the sensor assembly 34 to digital signals that can be
communicated to the data processor 20 via the data bus 16. In an
alternate embodiment, the analog-to-digital converter 24 may be deleted,
where the sensor assembly uses digital sensors with digital signal output
(e.g., transistor-to-transistor logic level (TTL) output).

[0019]The data processor 20 comprises a microprocessor, a microcontroller,
a programmable logic array, a logic circuit, an application specific
integrated circuit (ASIC), or another device for processing data. The
data processor 20 further comprises a position detection module 22. The
position detection module 22 may comprise a look-up table, a logic
circuit, an equation, or software instructions for determining a position
of the movable member 40 with respect to a reference position or fixed
member 38. For example, the look-up table may comprise input data and a
corresponding output data, where the input data comprises a state of the
first magnetic sensor 32, states or levels of the sensor assembly 34, or
states or levels associated with sensors within the sensor assembly 34
and where the output data comprises a position of the movable member 40
with respect to a reference position.

[0021]The communications interface 14 may comprise a data port, an
input/output port, a transceiver or another device for facilitating
communication of position data 12 to a controller or another device. The
communications interface 14 may provide an interface to a vehicular data
bus, such as CAN (Controller Area Network) data bus, an Ethernet databus,
or the like.

[0022]For small axial displacements of the movable member 40 in a
direction from an intermediate position (e.g., as illustrated in FIG.
1B), the output of the first magnetic sensor 32 is a first state (e.g.,
high logic level or one) and secondary magnet 146 is aligned with (or
faces) at least part of the sensor assembly 34 and the secondary magnetic
field 157 is used for fine position calculations. For sufficient
displacement of the movable member 40 toward the right in FIG. 1B, the
output of the first magnetic sensor 32 is generally at or approaching a
second state (e.g., low level), distinct from the first state.
Accordingly, the output level or state of the first magnetic sensor 32
indicates whether the movable member 40 has moved in a first range of
axial positions or to a second range of axial positions. The first range
of axial positions is indicated by the first state of the first sensor
32, whereas the second range of axial positions is indicated by the
second state of the first sensor 32. Meanwhile, the data processor 20 or
position detection module 22 uses sensor data from the sensor assembly 34
to determine the exact or fine position of the movable member 40 (e.g.,
with respect to a fixed member 38).

[0023]In one embodiment, the total length of the sensor assembly 34 and
the distance between the magnets determine the maximum displacement of
movement (e.g., maximum axial displacement) of the movable member 40 that
can be measured. For example, the total length of the sensor assembly 34
is based on the linear distance or separation between the outermost
sensors that comprise the sensor assembly 34. The spacing or pitch
between the adjacent sensors in the array (of the sensor assembly 34) is
proportional to or commensurate with the resolution (e.g., maximum
resolution) of the determined position. Here, an illustrative pitch or
spacing of approximately 10 mm between sensors in the array may support
determination of resolution with approximately 50 micrometer accuracy,
for instance.

[0024]The magnetic field (e.g., first magnetic field 55 or secondary
magnetic field 157) of a single magnet (e.g., first magnet 42 or
secondary magnet 146) may be measured by multiple sensors in the sensor
assembly 34 simultaneously to produce a target level of accuracy and
reliability in the determined position of the movable member 40. Each of
the sensors in the sensor assembly 34 may detect the magnitude of the
magnetic field, the direction or angle of the magnetic field, or both.
The data processor 20 may evaluate the magnitude of the magnetic field
detected at each sensor in the array, the angle or direction of the
magnetic field, or both as input. The data processor 20 may derive the
axial position of the movable member 40 from an equation, a look-up
table, a chart, a database or another technique based on the magnitude of
the magnetic field, the angle of the magnetic field, or both.

[0025]For example, the data processor 20 may store reference magnitude
data, reference angular data, or both on the detected or received
magnetic field (composed of the relative contributions from fields 55 and
157) for each sensor in the assembly 34 at a variety of known or
incremental axial positions of the movable member 40 with respect to the
fixed member 38. The reference magnitude data, reference angular data, or
both may be referred to as position data 12 or reference position data.
The data processor 20 can determine a position of the movable member 40
by searching for a match or closest match of the detected magnitude data,
detected angular data, or both on magnetic fields (for each sensor in the
sensor assembly 34) with the reference magnitude data, reference angular
data, or both for corresponding known axial positions of the movable
member 40 with respect to the fixed member 38.

[0026]The first magnetic sensor 32 supports a reduction in the number of
sensors (e.g., analog sensors) within the sensor assembly 34 that might
be otherwise required to achieve a comparable resolution (e.g., 50
micrometer resolution where the pitch or separation between adjacent
sensors in the array is approximately 10 mm) in position determination.
The sensors in the sensor assembly 34 are readily operated in the
saturated mode readout method to reduce the sensitivity to temperature
and vibration effects. Further, by sensing magnetic fields, the sensing
system 11 does not have contacting parts that might be disrupted,
misaligned, or improperly calibrated because of radial gap variation,
fabrication tolerances or wear.

[0027]The position detection system 111 of FIG. 2A and FIG. 2B is similar
to the position detection system 11 of FIG. 1A and FIG. 1B, except the
position system 111 further comprises a second magnetic sensor 132 and a
total of three magnets secured to the movable member 40. For the position
detection system 111, the three magnets shown in FIG. 2B shall be
referred to as the first magnet 42, the second magnet 46 and the third
magnet 44. As shown, the first magnet 42 is positioned at a first axial
position; the second magnetic 46 is positioned at a second axial position
65; the third magnet 44 is positioned at an intermediate axial position
63. Like reference numbers in FIG. 1A, FIG. 1B, FIG. 2A and FIG. 2B
indicate like elements.

[0028]In accordance with one embodiment of the invention, FIG. 2A and FIG.
2B show a system 111 for determining the position of a movable member 40
(FIG. 2B) with respect to a stationary or fixed member 38. In FIG. 2B,
the first magnet 42, the second magnet 46 and the third magnet 44 are
secured to the movable member 40 and spaced apart from each other.

[0029]The position detection system 111 comprises a group of magnetic
field sensors: a first magnetic sensor 32, a second magnetic sensor 132,
and a sensor assembly 34. The first magnetic sensor 32 and the second
magnetic sensor 132 may be coupled to a data bus 16. The sensor assembly
34 has sensor output coupled to a signal conditioner 28. The signal
conditioner 28 is coupled to an analog-to-digital converter 24. In turn,
the analog-to-digital converter 24 is coupled to a data bus 16.

[0030]A data processor 20 can communicate with one or more of the
following components via the data bus 16: the first magnetic sensor 32,
the second magnetic sensor 132, the analog-to-digital converter 24, a
data storage device 10 and a communications interface 14. As illustrated
in FIG. 2A, the data processor 20, the data storage device 10, and the
communications interface 14 are coupled to the data bus 16. The data
processor 20 comprises a position detection module 22. The data storage
device 10 may store position data 12 or calibration data 12, or both,
determined by the data processor 20 or position detection module 22.

[0031]The first magnetic sensor 32 and the second magnetic sensor 132 each
may comprise one or more of the following: a digital magnetic field
sensor, an analog magnetic field sensor with an integrated
analog-to-digital converter 24, a magneto-resistive sensor, a Hall-effect
sensor, a linear position magnetic sensor, or an angular position
magnetic sensor. In one embodiment, the digital magnetic field sensors
have one of two discrete states or output levels. For example, the output
levels (e.g., voltage levels or logic levels) may represent a low logic
level (e.g., 0) or a high logic level (e.g., 1). In one configuration,
the output level of the first magnetic sensor 32 provides a signal or
data output that indicates whether or not a magnet (e.g., 42, 44 or 46)
on the movable member 40 is in close proximity to the first magnetic
sensor 32. Similarly, the output level of a second magnetic sensor 132
provides a signal or data output that indicates whether or not a magnet
(e.g., 42, 44 or 46) on the movable member 40 is in close proximity to
the second magnetic sensor 132. Accordingly, the data output of the first
magnetic sensor 32, the second magnetic sensor 132, or both, may be used
to determine the direction of displacement of the movable member 40
(e.g., from an intermediate axial position 63 or another reference
point). If the magnetic field of at least one magnet (e.g., 55, 57, or
59) is received or detected with sufficient field strength for at least
some sensors (e.g., analog sensors) within the sensor assembly 34, the
sensor assembly 34 provides position data (e.g., or fine position data).

[0032]In a first exemplary configuration, the first magnetic sensor 32 has
an output (e.g., a digital output), where a first state (e.g., high logic
level) indicates that a magnetic field (e.g., first magnetic field 55 of
a first magnet 42) meets or exceeds a threshold magnetic field strength,
and where a second state (e.g., low logic level) indicates that a
magnetic field less than the threshold magnetic field strength is present
or no detectable magnetic field is present. Conversely, the second
magnetic sensor 132 has an output (e.g., a digital output), where a first
state indicates that a magnetic field (e.g., second magnetic field 59 of
a second magnet 46) meets or exceeds a threshold magnetic field strength,
and where a second state indicates that a magnetic field less than the
threshold magnetic field strength is present or that no detectable
magnetic field is present

[0033]In a second exemplary configuration, the first magnetic sensor 32
and the second magnetic sensor 132 have a first group of states
indicative of one direction of displacement of the movable member 40; the
first magnetic sensor 32 and the second magnetic sensor 132 have a second
group of states indicative of an opposite direction of displacement of
the movable member 40, where the first group and the second group are
distinct from each other. For example, if the movable member 40 is moved
to the left in FIG. 2B, the first group of states may comprise the first
magnetic sensor 32 having a first state (e.g., high logic level) and the
second magnetic sensor 132 having a second state (e.g., low logic level),
distinct from or opposite of the first state. Similarly, if the movable
member 40 is moved to the right in FIG. 2B, the second group of states
may comprise the first magnetic sensor 32 having a second state (e.g.,
low logic level) and the second magnetic sensor 132 having a first state
(e.g., high logic level), distinct from or opposite of the second state.

[0034]The sensor assembly 34 comprises an array of magnetic field sensors.
For example, the sensor assembly 34 comprises a generally linear array of
magnetic field sensors, where each sensor is separated from an adjacent
sensor by a known or fixed interval. Each magnetic field sensor within
the sensor array may comprise an analog sensor, a magneto-resistive
sensor, a Hall-effect sensor, a linear position magnetic sensor, or an
angular position magnetic sensor. The output of each analog sensor is
proportional to the magnetic field (e.g., from the magnets moving on the
rod) and can be used to determine a position of the movable member 40
with a resolution that is much smaller than the distance between two
sensors (e.g., typically 50 micrometers for a 10 mm pitch) on the movable
member 40.

[0035]In one embodiment, the signal conditioner 28 has conditioner inputs
for receiving sensor data from each magnetic sensor in the sensor
assembly 34. The signal conditioner 28 is coupled to the
analog-to-digital converter 24. The analog-to-digital converter 24 is
coupled to a data bus 16.

[0036]The data processor 20 comprises a microprocessor, a microcontroller,
a programmable logic array, a logic circuit, an application specific
integrated circuit (ASIC), or another device for processing data. The
data processor 20 further comprises a position detection module 22. The
position detection module 22 may comprise a look-up table, a logic
circuit, an equation, or software instructions for determining a position
of the movable member 40 with respect to a reference position or fixed
member 38. For example, the look-up table may comprise input data and a
corresponding output data, where the input data comprises a state of the
first magnetic sensor 32, a state of the second magnetic sensor 132, and
levels (e.g., magnetic field strengths or angular orientation of magnetic
fields) associated with the sensor assembly 34 and where the output data
comprises a position of the movable member 40 with respect to a reference
position.

[0037]The position sensing system 111 of FIG. 2A and FIG. 2B may support
up to three ranges of axial displacements of the movable member 40 with
respect to a fixed member 38. The three ranges may be contiguous or the
ranges may overlap. For a primary range of small axial displacements of
the movable member 40 in a direction from an intermediate axial position
63, the output of the first magnetic sensor 32 is a first state (e.g.,
high logic level or one) and the second sensor is at a first state (e.g.,
a high logic level or one); the intermediate magnet or third magnet 44 is
aligned with (or faces) at least a portion of (e.g., some sensors in) the
sensor assembly 34 and the third magnetic field 57 is used by the sensor
assembly 34 and the data processor 20 for fine position calculations.

[0038]For a secondary range of displacements of the movable member 40
toward the first magnetic sensor 32 (or to the left as illustrated in
FIG. 2B), the output of the first magnetic sensor 32 is generally at or
approaching a first state (e.g., high level or one), whereas the output
of the second magnetic sensor 132 is generally at a second state (e.g.,
low level), distinct from the first state. For the secondary range (e.g.,
where the movable member 40 is shifted slightly to the left, such that
the second sensor 132 is no longer aligned with the second axial position
65) the second magnetic field 59 of the second magnet 46 is detected by
one or more sensors of the sensor assembly 34 and the third magnetic
field 57 of the third magnet 44 is detected by the first magnetic sensor
32.

[0039]For a tertiary range of displacements of the movable member 40
toward the second magnetic sensor 132 (or the right as illustrated in
FIG. 2B), the output of the second magnetic sensor 132 is generally at or
approaching a first state (e.g., high level), whereas the output of the
first magnetic sensor 32 is generally at a second state (e.g., low
level), distinct from the first state. For the tertiary range (e.g.,
where the movable member 40 is shifted slightly to the right such that
the first sensor 321 is no longer aligned with the first axial position
61) the first magnetic field 55 of the first magnet 42 is detected by one
or more sensors of the sensor assembly 34 and the third magnetic field 57
of the third magnet 44 is detected by the second magnetic sensor 132.
Accordingly, the output level or states of the first magnetic sensor 32
and the second magnetic sensor 132 collectively indicate whether the
movable member 40 has moved to the left, right (e.g., in a secondary or
tertiary range, respectively) or remains within a range of an
intermediate position (e.g., centered or initial position).

[0040]The first magnetic sensor 32 and the second magnetic sensor 132
facilitate the determination of the direction of movement of the movable
member 40. In contrast, the sensor assembly 34 provides information
associated with determining a position (e.g., a fine or precise position)
of the movable member 40 with respect to the fixed member 38. The total
length of the sensor assembly 34 (or its sensors) and the distance
between the first and second magnets determine the maximum displacement
or movement (e.g., maximum axial displacement) of the movable member 40
that can be measured.

[0041]The spacing or pitch between the adjacent sensors in the array of
the sensor assembly 34 is proportional to or commensurate with the
resolution (e.g., maximum resolution) of the determined position. For
example, although other configurations are possible and fall within the
scope of the claims, if the sensor assembly 34 comprises seven sensors
(e.g., analog magneto-resistive sensors) spaced apart by a pitch of 10
mm, the sensing system 11 may be used to determine position over
approximately 70 mm. Further, the resolution of the determined position
will be commensurate or proportional to the spacing or pitch between the
sensors. Here, an illustrative pitch or spacing of approximately 10 mm
between sensors in the array may support determination of resolution with
approximately 50 micrometer accuracy.

[0042]The magnetic field of one or more magnets (e.g., the third magnetic
field 57 of the third magnet 44) may be measured by multiple sensors in
the sensor assembly 34 simultaneously to produce such accuracy. Each of
the sensors in the sensor assembly 34 may detect the magnitude of the
detected magnetic field, the direction or angle of the detected magnetic
field, or both. The detected magnetic field may comprise contributions
from one or more of the following: the first magnetic field 55, the
second magnetic field 59 and the third magnetic field 57. The data
processor 20 may evaluate the magnitude of the detected magnetic field
that is detected at each sensor in the array of sensors within the sensor
assembly 34, the angle or direction of the magnetic field, or both as
input data.

[0043]The data processor 20 may derive the axial position of the movable
member 34 from an equation, a look-up table, a chart, a database or
another technique based on the foregoing input data. For example, the
data processor 20 may store reference magnitude data, reference angular
data, or both on the magnetic field for each sensor in the assembly 34 at
a variety of known or incremental axial positions of the movable member
40 with respect to the fixed member 38. The data processor 20 can
identify a position of the movable member 40 by searching for a match or
general equivalence (e.g., within a certain target tolerance) of the
detected magnitude data, angular data, or both on magnetic fields (for
each sensor in the sensor assembly 34) with the reference magnitude data,
reference angular data, or both for corresponding known axial positions
of the movable member 40 with respect to the fixed member 38.

[0044]The first magnetic sensor 32 and the second magnetic sensor 132
support a reduction in the number of analog sensors within the sensor
assembly 34 that might be otherwise required to achieve a comparable
resolution (e.g., 50 micrometer resolution where the pitch or separation
between adjacent sensors in the array is approximately 10 mm) in position
determination. The sensors in the sensor assembly 34 are readily operated
in the saturated mode readout method to reduce the sensitivity to
temperature and vibration effects. Further, by sensing magnetic fields,
the sensing system 11 does not have contacting parts that might be
disrupted, misaligned, or improperly calibrated because of radial gap
variation, fabrication tolerances or wear.

[0045]The sensing system 211 of FIG. 3 is similar to the sensing system
111 of FIG. 2A and FIG. 2B, except the sensing system 211 of FIG. 3
further comprises a first logic circuit 18, a second logic circuit 30,
and multiple rows (e.g., three rows) of first magnetic sensors 32, second
magnetic sensors 132 and sensor assemblies 34. Like reference numbers in
FIG. 2A, FIG. 2B and FIG. 3 indicate like elements.

[0046]In FIG. 3, there are three rows (135, 137, and 139) or strips of
first magnetic sensors 32, second magnetic sensors 32 and sensor
assemblies 34. However, in alternate embodiments two or more rows of
first magnetic sensors 32, second magnetic sensors 132 and sensor
assemblies 34 may be used. Multiple rows of first magnetic sensors 32,
second magnetic sensors 32 and sensor assemblies are well-suited for
enhancing reliability and providing redundancy to protect against
circuitry or sensor failure of the first magnetic sensors 32, the second
magnetic sensors 132, and sensors within the sensor assemblies 34. Here,
the multiple rows are referred to as a first row 135, a second row 137,
and a third row 139.

[0047]As shown, the first magnetic sensors 32 are coupled to a first logic
circuit 18. The second magnetic sensors 32 are coupled to a second logic
circuit 30. Each sensor assembly 34 is coupled to a signal conditioner
28.

[0048]In one embodiment, each logic circuit (18, 30) may comprise an AND,
NAND, NOR, OR gate or another logic function. For example, if the first
logic circuit 18 comprises a multiple input AND gates, each of the first
sensor assemblies 32 must provide the same input to produce a desired
logic level (e.g., high or logic level 1) at the output of the first
logic circuit 18. Similarly, if the second logic circuit 30 comprises a
multiple input AND gates, each of the second sensor assemblies 132 must
provide the same input to produce a desired logic level (e.g., high or
logic level 1) at the output of the second logic circuit 30.

[0049]In an alternate embodiment, the first logic circuit 18 and the
second logic circuit 30 may be omitted, such that the first magnetic
sensors 32 are coupled, directly or indirectly, to the data bus 16 and
such that the second magnetic sensors 132 are coupled, directly or
indirectly, to the data bus 16.

[0050]The data processor 20 or position detection module 22 may determine
the position of the movable member even if only one row (135, 137 or 139)
of sensors is functioning or if only one first sensor 32, one second
sensor 36 and a single sensor assembly 34 from multiple rows is
functioning. If multiple rows are functioning (135, 137 and 139), the
position determination module may determine a mean or average position
based on sensor readings from multiple rows (135, 137 and 139).
Accordingly, the redundancy afforded by multiple rows of sensors (e.g.,
32, 132 and 34) provides increased reliability and immunity against
mechanical shock, vibration, and thermal stress.

[0051]The sensing system 311 of FIG. 4 is similar to the sensing system
211 of FIG. 3, except the sensing system 311 of FIG. 4 further comprises
each sensor assembly 34 associated with a corresponding different signal
conditioning circuit (328, 128, or 228) and a different analog-to-digital
converter (324, 124 or 224). Like reference numbers in FIG. 3 and FIG. 4
indicate like elements.

[0052]In FIG. 4, a first sensor assembly 334 may be coupled to first
signal conditioner 328. A second sensor assembly 134 is coupled to a
second signal conditioner 128. A third sensor assembly 234 is coupled to
a third signal conditioner 228. The first analog-to-digital converter
324, the second analog-to-digital converter 124 and the third
analog-to-digital converter 224 are coupled to the data bus 16.

[0053]In FIG. 4, the first row 235 comprises a first magnetic sensor 32,
the first sensor assembly 334, and a second magnetic sensor 36. The
second row 237 comprises a first magnetic sensor 32, the second sensor
assembly 134, and a second magnetic sensor 36. The third row 237
comprises a first magnetic sensor 32, the third sensor assembly 234, and
a second magnetic sensor 34. Further, each row (235, 237 and 239) of the
sensors may have one or more of the following features for redundancy or
enhanced reliability: (a) a separate connector, (b) a separate wire
harness, (c) a separate power supply circuit, and (d) a separate
controller or data processor.

[0054]In an alternate embodiment, multiple data processors 20 or one data
processor per corresponding analog-to-digital converter could be used.

[0055]The sensing system (11, 111, 211 or 311) is well suited for
determining the position of a hydraulic cylinder for steering of heavy
equipment, agricultural, forestry, construction, or mining equipment.
Further, the sensing system 11 may be used with a hydraulic cylinder
associated with a boom or bucket of equipment to precisely control the
movement or position of the boom or a bucket.

[0056]Having described the preferred embodiment, it will become apparent
that various modifications can be made without departing from the scope
of the invention as defined in the accompanying claims.